Almost all alcohol treatment outcome studies use exclusion criteria to determine which subsample of patients will participate in research protocol. Although such exclusions are sometimes necessary for scientific, practical or ethical reasons, they may lower external validity to an unknown extent by creating an unrepresentative research sample. The purpose of this project is to provide a comprehensive assessment of exclusion criteria employed during the modern history of alcohol treatment outcome research. Specifically, we will examine which exclusion criteria have been utilized in treatment outcome research, how they have affected the generalizability of results, whether they have disproportionately excluded members of vulnerable populations (e.g., African-Americans, women) from research participation, and how they may have affected outcome results. To pursue these objectives, the nature and prevalence of exclusion criteria will be assessed using a meta-analytic data set comprising 701 alcohol treatment outcome studies conducted since 1970. The exclusion criteria in this data will be operationalized and applied to six large "real world" data sets comprising about 20,000 individuals seeking treatment for alcohol problems in different parts of the United States. Through this analytic procedure, we will be able to determine what proportion of real-world alcohol patients do not pass typical research exclusion criteria, and whether, under various exclusion criteria, the baseline and follow-up characteristics (e.g., outcomes) of excluded patients differ from those not excluded from outcome research studies.